The present invention pertains to an arrangement in an apparatus or a machine operated from the mains for the transfer of control commands to at least one working means in the apparatus or machine, such as a motor or the like, via a wire also used for the power supply to the working means. The arrangement includes a control unit provided for creating a control command by suppressing, in a predetermined order, at least part of one or several consecutive half-periods of a predetermined polarity of the supply voltage, and a slave unit operating in response to the control command transmitted to activate the working means.
In the U.S. Pat. Nos. 4,007,458 and 4,131,882 there are disclosed arrangements as described above. However, in these references the arrangements have been used in irrigation systems including a great number of valves and the object has been to convey out, in a simple way by means of the power supply cable, control commands for the control of the different valves.
If an arrangement of the kind described is to be used in an apparatus or a machine having several working means with inductive properties, such as motors, it has been difficult for the slave unit to interprete the control command if being sent while any such inductive working means is operating. The change in a number of half-cycles, obtained by suppressing of at least part of the cycle, is counteracted by the repugnance of the working means against changes and, as a result, the slave unit will experience difficulties in unambiguously identifying a control command being sent.